FAQ on: Allergy Concerns and the mRNA COVID-19 Vaccine

in Food Allergy
Published: December 16, 2020
Doctor with mask holding a covid-19 vaccine.
Photo: Getty

Updated May 17, 2022 The Centers for Disease Control and Prevention reports that more than 220.7 million people across the United States have had two shots of a COVID-19 mRNA vaccine as of May 17, 2022. As the vaccination and booster program to control the coronavirus continues, U.S. health agencies are monitoring any adverse effects.

In the allergy community, safety questions about the Pfizer-BioNTech and Moderna messenger RNA vaccines have arisen because of a small number of cases of severe reactions. A CDC detailed review of reported cases of anaphylaxis offered reassurance that such reactions are uncommon. It found only 66 cases of anaphylaxis among 17.5 million doses of the two vaccines administered.

Forty-seven of the anaphylactic reactions in adults were to the Pfizer-BioNTech vaccine, or 4.7 cases for every 1 million people who got that shot. With Moderna, the CDC study authors said there were 19 confirmed reports of anaphylaxis, or 2.5 cases for every 1 million people. The review, published in the journal JAMA, says the CDC’s continuing safety monitoring confirms “that anaphylaxis following vaccination is a rare event.”  

As we discuss in a separate news report here, the majority of those few cases involved women and those with allergy histories. 

Yet, even at the slightly higher rate of anaphylaxis with the Pfizer vaccine, 999,995 of 1 million Americans had that vaccine with no anaphylaxis. Those who did have a severe reaction were treated and recovered. [For allergy information on the Johnson & Johnson vaccine, see this article.]

Dr. Nancy Messonnier, former director of CDC’s National Center for Immunization and Respiratory Diseases, called anaphylaxis to either of the two mRNA vaccines “exceedingly rare.” The CDC stresses that these are safe vaccines and that, when weighing benefits and risks, the COVID-19 virus remains the far greater health risk. To date, the virus has claimed the lives of just under one million American citizens.

Although the number of reported cases of anaphylaxis to the mRNA vaccines remains small relative to the shots administered, Dr. Alkis Togias with the National Institute of Allergy and Infectious Diseases (NIAID) told Allergic Living about a nationwide clinical trial involving people with a history of severe allergic reactions. The study’s aim was to find out whether people with allergies – from foods to medications, insect stings or mast cell disorders – were at any higher risk of a reaction to the mRNA vaccines than those without allergies. [Update:] The May 2022 results concluded these study participants weren’t at higher risk of reaction.

Debate About Polyethylene Glycol

On Dec. 14, 2020, the Pfizer BioNTech vaccine began being administered in the U.S., first to health-care workers. On Dec. 15, a nurse at a hospital in Juneau, Alaska, became the first reported American case of anaphylaxis to the Pfizer vaccine. She was treated with epinephrine and recovered.

The CDC says it is safe for those with a history of severe allergies to foods or drugs to get the Pfizer and Moderna vaccines. But it advises that there should be an observation period, and epinephrine must be available. The advice is to monitor for 15 minutes, but there’s a longer period for those with a history of anaphylactic reactions. “Vaccine providers should observe patients with a history of anaphylaxis (due to any cause) for 30 minutes after vaccination,” the agency says.

The authors who reviewed the anaphylaxis reports also say that “all facilities administering COVID-19 vaccines should have the necessary supplies and trained medical personnel available to manage anaphylaxis.”

When it comes to triggers of the anaphylaxis cases following mRNA vaccine administration, there has been considerable debate about polyethylene glycol (or PEG), since it is a component of both the mRNA vaccines. The CDC advises those with a known allergy to PEG not to get the vaccine. Yet, while PEG is implicated in unrelated cases of medication anaphylaxis, it’s an uncommon allergy, says Dr. Kimberly Blumenthal, a drug allergy expert at Massachusetts General Hospital.

There is no confirmation that PEG has triggered any of the mRNA vaccine reactions so far. As well, two experts told Allergic Living they expect there is likely more than one cause of these severe reactions. A couple of other likely culprits are not allergy-based, but have symptoms that look much like anaphylaxis.

Importantly, Blumenthal reminds that “allergy to a food doesn’t mean you are allergic to drugs. Allergy to drugs doesn’t mean you are allergic to vaccines.”

In this article, Allergic Living recaps what is known so far of any risks or allergy precautions with mRNA vaccines, along with answers to some frequent questions. This post is being updated regularly.     

Who Should Not Get a COVID-19 mRNA Vaccine?

The CDC says that for either the Pfizer-BioNTech or Moderna vaccines, you should not get the vaccine if you:

• Had anaphylaxis following a previous dose of an mRNA COVID-19 vaccine or any of its components. (Each of these mRNA vaccines involve two doses, given a few weeks apart.)

• Had an immediate (or IgE-based) allergic reaction* of any severity to a previous dose of an mRNA COVID-19 vaccine or any of its components, including polethylene glycol (or PEG).

• Had an immediate allergic reaction of any severity to polysorbate (which can cross-react with PEG, a vaccine component).

Qualifications: The CDC qualifies the last 2 points to say that people who fit those definitions “should not receive mRNA COVID-19 vaccination unless they have been evaluated by an allergist-immunologist and it is determined that the person can safely receive the vaccine (e.g. under observation, in a setting with advanced medical care available).”

Additionally, the agency says your health-care provider (e.g. allergist) should help to determine whether a reaction after vaccination is truly an “immediate allergic reaction” as opposed to post-vaccination side effects, some of which were seen in the clinical trials. (In other words, you might still qualify for the shot to protect against COVID-19.)

The CDC counsels caution when considering vaccination for:
A person with a history of anaphylaxis to another vaccine or a history of anaphylaxis to an injectable medication that’s not related to a component of mRNA vaccines or polysorbate.

The agency says such patients may want to consult an allergist for advice about potential risks and balance these against the benefits of vaccination. Factors the CDC says allergists and patients with a history of a vaccine/injectable severe reaction should consider include:  

  • The risk of exposure to COVID-19 because of a living situation (e.g. a long-term care home) or because of job-related risk.
  • The risk of a severe case of coronavirus disease because of age or medical conditions.
  • The unknown risk of anaphylaxis after an mRNA COVID-19 vaccination for a person with a history of an immediate allergic reaction to other vaccines or injectable medications.
  • Will the patient be vaccinated in a setting where appropriate medical care is immediately available for anaphylaxis?

*The CDC defines an “immediate allergic reaction” as one that involves symptoms such as widespread hives, swelling and respiratory distress (such as wheezing).

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Can I get the COVID-19 vaccine if I’ve got food allergy, drug allergy, latex allergy or insect allergy?

The short answer is yes. In its guidance to doctors on the Pfizer and Moderna vaccines, the CDC says:

1. There is no restriction in the U.S. on receiving the mRNA COVID-19 vaccines for anyone who has:

• A history of food, pet, insect, venom, environmental (e.g. pollen, dust) or latex allergies.
• A history of allergy to oral medications.
• Non-serious allergy to vaccines or other injectables (e.g. no anaphylaxis).
• Family history of allergies.

Post-Vaccination Observation:
The CDC’s guidance for post-vaccination observation says there should be a 30-minute observation period for:
• Persons with a history of an immediate allergic reaction of any severity to a vaccine or injectable therapy;
• And for persons with a history of anaphylaxis due to any cause.

For those who have allergies but have never experienced anaphylaxis, the observation period is 15 minutes, the same as for those with no allergy history.

Further to Food and Latex: The American College of Allergy, Asthma, and Immunology (ACAAI) notes that individuals with allergies to medications, foods, inhalants, insects, and latex “are probably no more likely than the general public to have an allergic reaction to the mRNA COVID-19 vaccines.” 

As well, allergy experts Allergic Living has interviewed emphasize that there are no food proteins among the ingredients of either of the mRNA vaccines. On latex, the CDC notes that the stoppers on the mRNA vaccine vials are not made of natural rubber latex.

The CDC stresses that health-care providers administering the vaccine must have emergency equipment available, including epinephrine and antihistamines, blood pressure cuffs, and timing devices to check pulses.

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Ingredients of the Two mRNA Vaccines

This information is from FDA briefing documents used in the agency’s independent reviews of the Pfizer BioNTech and Moderna COVID-19 vaccines.

The Pfizer-BioNTech COVID-19 Vaccine is a sterile, preservative-free, frozen suspension for muscle injection. 

• Active ingredient: modified messenger RNA (known as mRNA)

• Lipids or fats known by chemical names:
– ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis (ALC-3015)
– (2- hexyldecanoate), 2-[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide (ALC-0159)
– 1,2-distearoyl-snglycero-3-phosphocholine (DPSC)
– and cholesterol

• Salts:
– potassium chloride
– monobasic potassium phosphate
– sodium chloride
– dibasic sodium phosphate dihydrate

• Sucrose or sugar

The Moderna COVID-19 Vaccine is a preservative-free frozen suspension for muscle injection. 

• Active ingredient: modified messenger RNA (known as mRNA)

• Lipids or fats known by chemical names:
– (SM-102)
– 1,2-dimyristoyl-rac-glycero3-methoxypolyethylene glycol-2000 [PEG2000-DMG]
– cholesterol
– and 1,2-distearoyl-snglycero-3-phosphocholine [DSPC]

• Acid stabilizers: tromethamine and tromethamine hydrochloride

• Acids: acetic acid

• Salts: sodium acetate

• Sucrose or sugar

The lipids (or fats) in the ingredients serve as a slippery coating that helps to slide the vaccine into the cells. Neither vaccine contains food proteins.

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Is polyethylene glycol (PEG) to blame for the few anaphylaxis cases to the vaccines?

Polyethylene glycol (PEG) is a compound found in skin creams, medications and some constipation remedies. In rare cases, PEG has been known to set off severe allergic reactions. 

The Pfizer and Moderna shots both contain PEG, which is used to coat and protect each of the mRNA vaccines. There is much discussion of whether PEG is the possible cause of the COVID-19 vaccine reactions seen to date. There is no confirmation of that, and drug allergy experts have told Allergic Living that anaphylaxis to PEG is quite rare. (Read about other potential mRNA vaccine reaction causes here.)

A study led by allergists at Massachusetts General Hospital notes that an FDA review between 2005 and 2017 showed an average of just four cases of PEG anaphylaxis per year. The Mass General study says there are many formulations of PEG, and the component used in the mRNA vaccines “is different from the PEG used most commonly in other health-care products.” 

At present, the CDC is saying those with a history of an IgE-based allergic reaction to PEG or to polysorbate should not get either of these vaccines. (See above: Who should not get an mRNA vaccine.) Investigation continues into the cause of the few serious reactions to the COVID-19 vaccines.

The concern about polysorbate relates to possible cross-reactivity with PEG. Dr. Anna Wolfson, an allergist and drug allergy expert at Massachusetts General, explains that “at the molecular level, PEG and polysorbate look structurally similar. So if a person is allergic to PEG, their immune system may also mount a response to polysorbate.” And the reverse is also true, for the person with a known allergy to polysorbate.

The study authored by Wolfson, Blumenthal and colleagues offers guidance to allergists and patients. It recommends that if a patient has had a previous severe allergic reaction to PEG or a polysorbate, then see an allergist for skin-testing with PEG. If the test is positive, that person would not be a candidate for either of the mRNA vaccines.

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As PEG is a component of the mRNA vaccines, is that safe for people with soy allergy?

We put the polyethylene glycol (PEG) and soy allergy question to two experts: allergist and vaccine expert Dr. James Baker, director of the Mary H. Weiser Food Allergy Center at the University of Michigan, and Dr. Kimberly Blumenthal, allergist and the safety officer for allergy at Massachusetts General. Both say there is no soy protein or other food protein in the mRNA vaccines. 

“The PEG component of these vaccines are derivatives of soy sterols (lipids) that are not cross-reactive with soy proteins that cause soy allergy,” stresses Baker.

Blumenthal agrees, telling Allergic Living: “Soy allergy is from protein, never plant-derived fatty acids” (the ‘lipids’ that Baker references). Importantly, she adds as a drug allergy expert: “Soy-allergic patients tolerate PEG all the time.”

In rare cases, PEG has triggered allergic reactions. However, Baker notes: “PEG derivatives that cause allergies usually involve some different protein. For example, PEG-asparaginase, an anti-cancer drug, which is altered by complexing with PEG. There is no cross-reaction between soy allergy and allergy to other PEG-conjugated proteins.”

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Do these vaccines have any ingredients of concern to those with dairy allergy or alpha-gal allergy?

Several readers asked about dairy and gelatin in relation to either dairy allergy or alpha-gal allergy. The CDC specifically says no gelatin or preservatives are used in either of the mRNA vaccines. Dairy isn’t directly addressed, but the CDC says there are no special precautions for any food allergens.

We asked two allergist-immunologists at Massachusetts General Hospital to expand on the questions about dairy allergy and alpha-gal allergy safety. Dr. Anna Wolfson and Dr. Sarita Patil, who are respectively drug and food allergy researchers, said:

“Although a few other vaccines have listed bovine extracts in their ingredients, our review of the COVID-19 Pfizer and Moderna mRNA vaccines does not indicate the inclusion of cow protein ingredients. For instance, there no bovine ingredients similar to those implicated in the past in a small number of reactions to other vaccines.”  

They additionally make this observation: “Given that both dairy allergy and alpha-gal are not rare diagnoses, and patients with these conditions were not excluded from the large trials nor the current vaccination program, we would have expected any dairy/beef association to have arisen by now if it were the culprit allergen.” 

In keeping with the CDC, they say: “Our current recommendation is that patients with a history of anaphylaxis, which would include patients with severe dairy allergy and alpha-gal allergy, require 30 minutes of observation after getting an mRNA shot.”

And lastly say Wolfson and Patil, “we do not see an official constituent or chemical or stabilizer with cross-reactivity in vaccine ingredients to suggest that patients with specific food allergies need caution.” 

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Are the mRNA vaccines safe for people with egg allergy?

The CDC specifies that the two vaccines do not contain eggs.

“There is no egg or egg-related component of the RNA vaccines,” says Baker. “Therefore, these vaccines are totally safe for egg-allergic individuals.”

The egg allergy question likely arises in part because of common misunderstanding about this allergy in relation to the flu shot and the MMR vaccine. In both those cases, health authorities have investigated and recommend that these vaccines are safe and effective for those with egg allergy. For the flu shot see this link for the MMR see this link.

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Are the mRNA vaccines safe for people with celiac disease?

A group of leading North American celiac experts with the Society for the Study of Celiac Disease (SSCD) answers this question: 

“As the safety and efficacy data on COVID vaccination has emerged, there is no evidence to suggest that people with celiac disease would be more prone to an adverse effect of vaccination. Celiac disease is not considered an allergy, and by itself does not prompt additional precaution when proceeding with vaccination. Patients with concerns about vaccination and their particular circumstance should speak with their health-care provider.”

Additionally, the CDC says: “Persons with autoimmune conditions who have no contraindications to vaccination may receive an mRNA COVID-19 vaccine.”

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What severe reactions have occurred in the U.S.?

On Dec. 15, 2020, a nurse in Alaska became the first American to have an anaphylactic reaction to the Pfizer-BioNTech coronavirus vaccine. She got her shot at the Bartlett Regional Hospital in Juneau, where she works. The hospital emergency physician who treated her told a virtual press briefing (attended by Allergic Living) that the woman had a red rash on her face and experienced shortness of breath and an elevated heart rate. She was given epinephrine.

The nurse was admitted to the hospital, and put on an epinephrine drip and treated with steroids. A day later, she had recovered and was discharged.  

On Dec. 24, 2020, a Boston doctor became the first to experience anaphylaxis to the Moderna vaccine. The doctor, who experienced a drop in blood pressure, administered his own epinephrine auto-injector (which he carries due to a shellfish allergy). He recovered and was discharged.

On Jan. 6, 2021 in its first report on allergic reactions to the mRNA vaccines, the CDC gave some details on 21 confirmed anaphylactic reactions reported in the first 1.5 weeks of vaccination program. Given the context that those reactions were out of 1.9 million doses administered, the CDC said a severe reaction to the COVID-19 vaccine “appears to be a rare event.” (The rate of reaction has further decreased.)

Of the 21 patients who developed anaphylaxis (which includes the Alaska nurse but not the Boston doctor), 17 had history of allergies or allergic reactions to drugs or to foods or insect stings. There was no common allergen, and all recovered with treatment. Most received epinephrine.

The CDC’s Jan. 6 COVID-19 vaccine allergic reactions report says:

• 7 of the patients reported having anaphylaxis in the past. The triggers for the anaphylaxis varied among the patients. There was previous anaphylaxis to: a rabies vaccine, sulfa drugs, a jellyfish sting, walnuts, an anti-nausea medication, a flu vaccine and one case was unspecified.
• 90% of the anaphylaxis patients were women, however 65% of those vaccinated were also women.
• The median age was 40 years old; there were no clusters of reactions by geography.

It’s important to keep in mind the level of attention for the COVID-19 vaccine rollout. While it is not unusual to have a small percentage of reactions to drugs or vaccines, “never before has a vaccine received this level of public scrutiny,” says pediatric allergist and researcher Dr. Brian Vickery. “This is the first social media pandemic.”

Messonnier, the former CDC immunization director, says: “The known and potential benefits of the current COVID-19 vaccines outweigh the known and potential risks of getting COVID-19.” As of May 17, 2022, the CDC’s tracking shows there have been 82.5 million total reported coronavirus cases in the USA – and that 997,468 people have died of the virus.

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What exactly is an mRNA vaccine?

In large clinical trials, the mRNA vaccines proved highly effective in preventing the coronavirus. The Pfizer shot had 95% efficacy in its study, while the Moderna vaccine had an efficacy rate of 94.1%. But how do these novel therapies work with the immune system?

To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. But mRNA vaccines work differently and contain no live virus.

The CDC explains that these vaccines instead “teach our cells how to make a protein – or even just a piece of a protein – that triggers an immune response.” This leads the immune system to produce antibodies against the virus, which will protect an inoculated person who gets exposed to the real virus.

When a COVID-19 mRNA vaccine is injected into the arm muscle, the CDC explains that the mRNA gives “instructions for our cells to make a harmless piece of what is called the ‘spike protein.’ The spike protein is found on the surface of the virus that causes COVID-19.”

After the protein piece is made, the CDC says a cell will destroy the genetic material from the vaccine. Next, when cells display the protein, “our immune systems will recognize that the protein doesn’t belong there and begin building an immune response and making antibodies, like what happens in natural infection against COVID-19.”

A few weeks after vaccination, the body is left with a supply of white blood cells – “memory” T-lymphocytes as well as B-lymphocytes – that will know to fight the virus.  

Allergist Dr. David Stukus, an associate professor of pediatrics at Nationwide Children’s Hospital, explains that “the mRNA part is just a blueprint, it’s harmless.” After we inject it into our bodies and the spike protein is built, “our immune systems, which are so robust, recognize that foreign antigen. Then if we encounter the spike protein in real life, our immune system says, ‘Hey, you don’t belong here,’ and we can mount a very rapid and protective antibody response.”

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During clinical trials for the mRNA vaccines, what reactions and side effects were seen? 

In Pfizer’s clinical trial of over 43,000 study participants who received either the vaccine or its placebo, data show some side effects. These include injection site pain, fatigue, headache, muscle or joint pain, chills or vomiting. The data further show a small number of suspected allergic reactions in both the vaccine and placebo groups, but at a rate of less than 1% (0.63% and 0.51% respectively).

The FDA conducted an independent analysis of Pfizer’s clinical trial results, and found a few instances of potential minor allergic reactions among participants. None were considered serious or required epinephrine.

In an FDA review of Moderna’s Phase 3 trial of just over 30,000 people who received two shots of either the vaccine or placebo, side effects included injection site pain, fatigue, headache, muscle or joint pain and chills.  

Bell’s Palsy fact-check: During the Pfizer trial, four cases of Bell’s palsy (temporary facial paralysis) emerged in the treatment group and there were four cases in the Moderna trial (three in the treatment group and one with a placebo patient).

The FDA says this may or may not relate to mRNA vaccination, and will continue to be monitored. The incidence for Bell’s palsy within 43,000 people involved in the Pfizer trial was actually lower than the normal incidence rate in the general population. In its report on the Pfizer vaccine, the FDA writes

“The observed frequency of reported Bell’s palsy in the vaccine group is consistent with the expected background rate in the general population, and there is no clear basis upon which to conclude a causal relationship at this time, but FDA will recommend surveillance for cases of Bell’s palsy with deployment of the vaccine.”

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Background on the vaccine emergency authorizations.

On Dec. 13, 2020, the CDC approved emergency use authorization (EUA) for the Pfizer-BioNTech mRNA vaccine, initially for those 16 years of age and older. This followed the FDA’s sanction for the EUA and positive independent expert reviews of the Pfizer vaccine’s clinical trial data. 

An independent panel advising the FDA reviewed the data on the Moderna mRNA vaccine and voted strongly to recommend the FDA give an EUA to the vaccine, initially for those 18 and older. On Dec. 18, 2020, the FDA gave its authorization, while an advisory committee to the CDC also voted strongly in favor of the authorization. The U.S. Moderna rollout began on Dec. 21, 2020. The vaccine authorizations would later be extended to those 12 and older.

On Aug. 23, 2021, the FDA officially approved the Pfizer-BioNTech vaccine for the prevention of COVID-19 disease in those 16 and older. (The EUA was extended for those 12 and older.)

In Britain, the initial vaccine rollout started on Dec. 8, 2020. In Canada, authorities authorized the Pfizer shot on Dec. 9, 2020, and later gave emergency approval to the Moderna vaccine as well.

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If you get an mRNA COVID-19 vaccine…

• If you have allergies, make them known to your health-care provider giving the shot. As mentioned in the section above on food, drug, latex and environmental allergies, only those with severe allergies to a component of the vaccine are specifically advised not to get it. (Anyone with a history of anaphylaxis should be monitored for 30 minutes after the shot, rather than the usual 15 minutes.)

If you have previously had a reaction to a vaccine other than this one, the CDC says you may be able to get an mRNA shot, but suggests reviewing the risks and benefits with your allergist.

• The CDC requires your health-care provider administering the vaccine to have emergency equipment available, including epinephrine and antihistamines, blood pressure cuff. While not required, the agency also prefers that additional tools are available, including: a pulse oximeter, oxygen, albuterol and intravenous fluids.

• After getting the first shot, the CDC asks you to register with V-safe, its smartphone monitoring program. It uses text messaging and web surveys to follow-up with vaccine recipients. Should you have any adverse side effects, V-safe lets you to report them to assist in data gathering awareness. 

For adverse effects of significance, the CDC says a representative will get in touch.

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If you get the vaccine and think you’re experiencing anaphylaxis…

If you have known allergies and believe you experiencing symptoms of anaphylaxis, follow your emergency care plan: use your epinephrine auto-injector, then call 9-1-1.

If you have never experienced a severe allergic reaction and don’t carry epinephrine: call 9-1-1 and mention this is an anaphylactic reaction and that you need an ambulance carrying epinephrine.

Post treatment: Your severe reaction should be reported through the CDC’s Vaccine Adverse Events Reporting System (VAERS). Health-care providers are required to report such adverse events.

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Should I get vaccinated if I’m pregnant or breastfeeding?

The CDC said in August 2021 that “evidence about the safety and effectiveness of COVID-19 vaccination during pregnancy has been growing. These data suggest that the benefits of receiving a COVID-19 vaccine outweigh any known or potential risks of vaccination during pregnancy.” The agency recommends pregnant women get the mRNA vaccines, noting that “pregnant and recently pregnant people are more likely to get severely ill with COVID-19” compared to those who are not pregnant.

The agency also recommends the vaccine for women who are breastfeeding. The CDC says: “recent reports have shown that breastfeeding people who have received mRNA COVID-19 vaccines have antibodies in their breastmilk, which could help protect their babies. More data are needed to determine what protection these antibodies may provide to the baby.”

The American Academy of Pediatrics (AAP), American College of Obstetricians and Gynecologists (ACOG) and other agencies who are maternal care experts are urging pregnant women and lactating women to get the COVID-19 vaccine. In a September 2021 consensus statement, they wrote:

“Maternal care experts want the best outcomes for their patients, and that means both a healthy parent and a healthy baby. Data from tens of thousands of reporting individuals have shown that the COVID-19 vaccine is both safe and effective when administered during pregnancy. The same data have been equally reassuring when it comes to infants born to vaccinated individuals. Moreover, COVID-19 vaccines have no impact on fertility.”

ACOG adds that: “acetaminophen is recommended for pregnant women who experience fever or if desired for other side effects. Check with your maternal care provider about any vaccine questions you have.

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Who was excluded from the Pfizer trial?

Contrary to some early reports, Pfizer told the FDA reviewing panel of experts that people with a history of severe food or drug allergies were not excluded from the vaccine’s Phase 3 trial.

So who was excluded? Those who had a past severe adverse reaction to any vaccine or to a component of this vaccine, said Pfizer’s senior vice president of vaccine clinical research and development.

Allergist Dr. David Stukus notes that clinical trials have strict inclusion and exclusion criteria. In research, “you’re trying to control for all confounding variables that you can. If you enroll someone who’s had anaphylaxis to a prior vaccine and then they have anaphylaxis to this vaccine, it just clouds all the data.” Stukus also stressed that “true anaphylaxis to any vaccine is rare.”

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Related Reading:
J&J Vaccine: Allergists Assess Safety and Reaction Risks
COVID-19 Vaccines: How to Tell an Allergy from a Side Effect; Plus ‘COVID arm’
Likely More than 1 Cause of COVID-19 Vaccine Reactions
CDC Update: Severe Reactions to COVID-19 Vaccines Are Rare, Women Most Affected
Some Reactions to Vaccines Expected; But Not Reason to Avoid Shot
CDC’s FAQ of General COVID-19 Vaccination Questions